A typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The HDA typically includes a disk drive base and a disk drive cover that together enclose at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The PCBA includes electronics and firmware for controlling the rotation of the spindle motor and for controlling the position of the HSA, and for providing a data transfer channel between the disk drive and its host.
The HSA includes an actuator arm, having an actuator arm tip to which a head gimbal assembly (HGA) is typically attached by a process known as “swaging.” The HGA typically includes a read head and a suspension assembly that suspends or supports the read head. However, in certain “depopulated” HSAs, a relatively inexpensive dummy mass may be swaged to an actuator arm tip instead of a relatively more expensive HGA, where the dummy mass does not support any read head. For example, a dummy mass may be swaged to an actuator arm tip in a depopulated HSA to add mass for balancing and/or for matching dynamic characteristics (to the known dynamic characteristics of the fully-populated HSA). For the purposes of this disclosure, such dummy masses will also be referred to as “suspension assemblies,” even though they do not support any read head, since such dummy masses are typically designed to closely match the HGA that they replace from the viewpoint of the swaging process.
The read head is typically attached to a distal end of the suspension assembly, and a supported end of the suspension assembly is attached to an actuator arm that extends from the head actuator. The suspension assembly typically includes a load beam constructed of light sheet steel that includes a bend region. The bend region of the load beam acts as a spring that forces the read head against the disk surface with a specific desired pre-load force (also known as the “gram load”). The air bearing provides a reaction force that opposes the pre-load force in equilibrium. The suspension assembly also typically includes a laminated flexure that is attached to the load beam and to which the read head is electrically connected.
The suspension assembly also typically includes (at its supported end) a suspension base plate, also known as a “swage mount.” The swage mount includes a flat flange portion and a protruding cylindrical hub portion or “swage boss.” The swage boss typically protrudes through a clearance hole in the load beam, and the flange is spot welded to the load beam.
In a typical “swaging” process to attach a suspension assembly to an actuator arm, the swage boss protrudes into a corresponding swage hole in a distal tip region of the actuator arm. A swage ball is then temporarily forced through the swage boss during assembly, causing the swage boss to plastically expand radially, and therefore radially interfere with the corresponding swage hole in the actuator arm tip. After swaging, the outer periphery of the swage boss tightly engages and is radially preloaded against the inner periphery of the corresponding swage hole in the actuator arm tip.
Various problems with this method of attaching HGAs to actuator arms have arisen. For example, the plastic deformation associated with swaging may cause undesirable variation in the gram load, with the tolerance for such variation becoming smaller as the data storage capacity of disk drives has increased and read heads have been miniaturized. Hence, there is a need in the art for a disk drive head stack design that may reduce gram load variation that results from swaging.
Moreover, swaging can be a relatively expensive and time-consuming process in the context of high volume manufacturing of disk drives. Therefore, from a manufacturing process time and cost perspective, single-pass swaging may be preferred. However, creating the necessary radial plastic deformation to create sufficient radial interference for a robust swage attachment, in a single pass, can be a relatively violent process that may lead to unacceptable gram load variation in a population of swaged HGAs. Multi-pass swaging, where the necessary total radial plastic deformation is created iteratively by swaging more than once with progressively larger swage balls and/or by forcing the swage ball(s) through the swage bosses in alternating directions, can be too time consuming and expensive a process for high volume manufacturing. Therefore, there is a need in the art for a disk drive head stack design that may reduce gram load variation that results from single-pass swaging.